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Full text of "Measurement of irrigation water on the farm"

UNIVERSITY OF CALIFORNIA 

COLLEGE OF AGRICULTURE 
AGRICULTURAL EXPERIMENT STATION 

CIRCULAR No. 250 
July, 1922 

MEASUREMENT OF IRRIGATION WATER ON THE FARM 

BY 

H. A. WADS WORTH 



CONTENTS 

PAGE 

Introduction 2 

Units of measurement and equivalents 3 

Weirs 4 

Rectangular weirs 7 

Cipolletti weirs 9 

90-degree triangular-notch weirs 11 

Weir construction 12 

Submerged orifices 14 

Submerged orifices of fixed dimensions 18 

Construction of submerged orifices of fixed dimensions 20 

Computations if tables are not available 20 

Adjustable submerged orifices 21 

Theory of inch box measurement 23 

Riverside box 24 

Anaheim Union Water Company measuring box 25 

Santa Ana Valley Irrigation Company miner's inch box 26 

Azusa hydrant 27 

Division boxes 29 

Mechanical devices for measuring water volumetrically 31 

Reliance meter 32 

Dethridge meter 33 

Other measuring devices 34 

Lyman meter 34 

Sentinel meter 34 

Venturi meter 34 

Venturi flume 35 

Summary 35 

TABLES 

1. Discharge table for rectangular weirs , 8 

2. Discharge table for Cipolletti weirs 10 

3. Discharge table for triangular notch 12 

4. Weir board dimensions 13 

5. Dimensions for weir boxes 14 

6. Discharge table for submerged orifices of fixed dimensions 19 

7. Dimensions for boxes for submerged orifices of fixed dimensions 20 



UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 



INTRODUCTION 

The aim of this circular is to make available in a single publi- 
cation the tables, and in some cases the formulae, necessary for the 
measurement of irrigation water under the varying conditions found 
in California. In order to avoid confusion, only those methods which 
are in common use have been considered in detail. 

Even with this limitation, it has been necessary to include a 
considerable number of methods of measurement. This is due to 
the variation in conditions under which irrigation water is delivered. 
As an example, in the Orland area in the Sacramento Valley, where 
field ditches are built on fairly steep grades, small weirs are used 
almost exclusively to measure irrigation water to the water user. 
In other areas where canal grades are much flatter and where the 
head of water in the canal is subject to wide fluctuations, the sub- 
merged orifice is used as a measuring device. In general these ori- 
fices are so built that the size of the orifice can be increased or de- 
creased as the changing head demands. In Imperial Valley, the 
submerged orifice has come into general use, largely because the water 
from the Colorado River is so heavily charged with silt that the use 
of weirs is unsatisfactory. 

The measurement of water in terms of the miner's inch is prac- 
tically universal in most of the foothill and citrus orchard sections 
of the state. In these areas, where irrigation water is bought and 
paid for on the basis of the miner's inch, special devices are in gen- 
eral use by which a flow can be measured directly in that unit with- 
out the necessity of transposing from the more common units of the 
other parts of the state. Where individual pumping plants are in 
use water is commonly measured in terms of gallons per minute. 

The common method of payment for irrigation water in an area 
has had a great influence in determining the method of measure- 
ment in that area. In most cases that method of measurement is 
used which can be most readily changed into the terms necessary 
for the computation of the water charges. 

In addition to descriptions of the devices used with these com- 
mon methods of measurement, which are familiar to most users of 
irrigation water, descriptions of a few unusual devices have been 
included, either because of the different theory involved, or because 
the devices seem well suited to a greater use in California. 



CIRCULAR 250] MEASUREMENT OF IRRIGATION WATER 3 

The tables for weir discharge and for flow through submerged 
orifices of fixed openings are the most recent and the most reliable 
that are available. The United States Reclamation Service and the 
United States Department of Agriculture, Division of Irrigation In- 
vestigations, have willingly furnished tables. 



UNITS OF WATER MEASUREMENT AND EQUIVALENTS 

Cubic foot per second. — This unit represents an exact and definite 
quantity of water, viz : the equivalent of a stream one foot wide and 
one foot deep flowing at the rate of one foot per second. 

24-hour second foot. — This is one cubic foot per second, running 
continuously throughout a 24-hour period. It is equivalent to ap- 
proximately two (exactly 1.9834) acre-feet. 

Acre-Foot. — This is the equivalent of a body of water one acre 
in area and one foot deep, or 43,560 cubic feet. One cubic foot per 
second, or fifty southern California inches, or forty California statute 
inches, running continuously for twenty-four hours will supply ap- 
proximately two (exactly 1.9834) acre-feet. 

Acre-Inch. — This is one-twelfth of one acre-foot, or the equivalent 
of a sheet of water one acre in area and one inch deep. It is the 
unit sometimes used instead of the acre-foot, especially in express- 
ing quantities of less than one acre-foot. One cubic foot per second 
running continuously for one hour will supply approximately one 
acre-inch. 

Gallon. — As many irrigators receive their water supply from 
pumps and as pump manufacturers usually estimate discharges in 
gallons per minute or per second, this is sometimes a convenient unit 
to use. One cubic foot is approximately equal to iy 2 gallons (ex- 
actly 7.4805) and one cubic foot per second is approximately equiva- 
lent to 450 gallons per minute or 7% gallons per second. 

One thousand gallons. — This unit is quite common in irrigation 
practice in San Diego County, California. 

Inch. — This is a variable unit having different meanings in dif- 
ferent states and even in different sections of the same state. The 
old miner's inch of California was the quantity of water flowing 
freely through an opening one inch square, the center of which was 
four inches below the surface of the water standing above the open- 
ing; it is equivalent to a flow of nine gallons per minute or 1/50 



4 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 

cubic foot per second. The present statute inch of California is 
denned as a flow of one and one-half cubic feet per minute. It is 
measured through an orifice one inch square under a six-inch pressure 
and is equivalent to a flow of 11% gallons per minute or 1/40 cubic 
foot per second. While the meaning of the inch varies with local prac- 
tice, it is not a stream of water one inch deep and one inch wide, regard- 
less of pressure. Where its meaning is clear, the inch is a convenient 
unit for measuring small streams up to, say 50 to 100 inches, and is 
quite frequently used for such streams, particularly on many of the 
southern California systems. For larger streams its use is generally 
discarded in favor of the more definite unit, cubic foot per second. 

24-hour inch. — This is a very common unit, especially in southern 
California, and is, as its name implies, one inch (the exact amount 
of which varies with locality and local custom) running for twenty- 
four hours. Variations of this unit found on some California irri- 
gation systems are the one-hour inch and the twelve-hour inch. 

The following table will be found useful in changing the ex- 
pression of a quantity of water from one of these units to another: 





Southern 

California 

miner's 

inch 


Statute 

miner's 

inch 


Gallons 

per 
minute 


Cubic feet 

per 

second 


Acre- 
inch 


Acre- 
foot 


1 southern Cali- 
fornia miner's 
inch equals.... 




1.25 


9.0 


fco 


1 in 50 
hours 


1 in 600 

hours 


1 Stat, miner's 
inch equals.... 


0.80 




11.25 


Ko 


1 in 40 
hours 


1 in 480 

hours 


1 gallon per 
minute equals 


tt 


ill. 25 




^450 


1 in 450 
hours 


1 in 5400 
hours 


1 cubic foot per 
second equals 


50 


40 


450 




1 in 1 
hour 


1 in 12 
hours 



WEIES 

A weir is one of the simplest and most accurate means of meas- 
uring irrigation water on the farm. The weir of the irrigation 
farmer is simply a bulkhead or wall placed across a stream, with an 
opening cut in the top through which the water is allowed to pass. 
This opening is commonly called the "weir notch." The depth of 
the water pouring through the weir notch is the measure of the 
amount of water in the stream. By gauging this depth and consult- 
ing the weir table for the kind and length of the weir notch used 
the amount of water passing over the weir is obtained. 



Circular 250] 



MEASUREMENT OF IRRIGATION WATER 



In some cases the weir bulkhead is placed in a short section of 
flume, called a weir box; in others it is placed directly across an 
earth ditch and is independent of any other structure. (Fig. 1.) The 
theory and method of weir measurement remain the same in either 
case. 

There are certain conditions which must be observed before a 
weir can be used for the accurate measurement of water. In general 




Fig. 1. Rectangular field weir in use. 



it may be said that the "weir crest" or bottom of the weir notch 
should be short enough so that the amount of water to be measured 
will never give a depth of less than two inches over the crest, and 
long enough so that the depth will never be more than one-third of 
the length of the crest. Care should also be taken to see that the 
weir crest is long enough so that the water can pour through the 
notch without having to back up in the channel to a greater height 
than can be done with safety to the ditch bank. A number of other 
conditions are usually laid down as necessary for the weir. The most 
important of these are as follows : 

1. The weir crest or bottom of the weir notch must be absolutely 
level. 



6 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 

2. The water passing over the weir must have a free "over-fall." 
If the water in the ditch below the weir is allowed to rise to such 
a height that this free fall is not possible, the weir is said to be sub- 
merged. Measurements made on a submerged weir are unreliable 
unless complicated corrections are introduced. 

3. The distance from the crest of the weir to the bottom of the 
canal or to the floor of the weir box above the weir crest need only 
be great enough to check the velocity of water flowing in the bottom 
of the stream, say about 0.5 foot for small weirs. 

4. The distance from the ends of the weir crest to the sides of 
the weir box or canal or ditch should be about twice the depth of the 
water on the weir, or, say from ten to twelve inches in the case of 
a weir with an eighteen-inch crest measuring about two cubic feet 
per second. 

5. The bottom and sides of the weir notch should have a narrow 
edge. The use of a galvanized iron crest to give such a narrow edge 
is quite common and very satisfactory but not necessary. Sometimes 
thin pieces of strap iron are fastened on the up-stream side of the 
weir notch. In other cases the board in which the weir notch is cut 
is merely beveled on the down-stream side to a crest thickness of 
one-eighth or one-quarter of an inch. 

6. Water should not be allowed to approach the weir with a ve- 
locity exceeding six inches per second. Also, it should flow to the 
weir in a smooth stream free from eddies or swirls. Both of these 
conditions are most easily met by placing the weir in a straight sec- 
tion of the ditch and, when necessary, by placing baffle boards across 
the channel. 

7. The depth of water on the weir crest must be measured suffi- 
ciently above the weir to be free from the downward curve of the 
water as it passes over the weir. For convenience in making this 
measurement of depth a stake with its top level with the crest of 
the weir is usually set at one side of the ditch two or three feet above 
the weir, the measurements of depth being made from the top of 
this stake to the surface of the water. 

It will be noted from these conditions that the weir is not a suit- 
able means of measuring water under all conditions. In ditches 
where the grade is very slight, placing a bulkhead across a stream 
and raising the level of the water above the weir often results in a 
break in the ditch bank. In such cases it is also difficult to keep the 
weir from becoming submerged. 

In streams heavily laden with silt the weir is not a practical 
means of measurement. Reducing the velocity of the water to the 



Circular 250] 



MEASUREMENT OF IRRIGATION WATER 



point necessary for weir measurements soon precipitates such a quan- 
tity of solid matter above the weir that suitable weir conditions no 
longer exist. 

By itself, a weir, measures a rate of flow and does not indicate 
the total quantity delivered. In conjunction with a water register, 
which keeps a graphic record of the changing depth of water over 
the weir, a permanent record is obtained from which the total quan- 
tity of water can be easily computed. 

WEIE NOTCHES 

There are three types of weir notches in common use, viz: rec- 
tangular weirs, Cipolletti weirs, and triangular weirs. Special tables 
have been devised for each of these. It is of course essential that 
the proper table be used for the weir crest selected.* 




Fig. 2. Two foot rectangular weir notch. 



RECTANGULAR WEIRS 

The name is taken from the shape of the weir notch, shown in 
figure 2. This weir is also known sometimes as the Francis weir. It 
is one of the earliest forms of weirs used and is the type from which 
all other forms have been developed. Because of the simplicity, ease 
of construction, and accuracy with which the crest and sides may be 
set with the implements ordinarily at hand, this type of weir should 
be used more widely than it has been in the past. It is as accurate as 
the other types. The crest is placed in a horizontal position and the 
sides extend vertically above the crest. A right angle is therefore 
formed, which permits the weir to be made and set easily and accu- 
rately by means of a carpenter's square and level. The sides must be 
placed carefully to give the desired length along the crest. Table 1 
gives the discharge over rectangular weirs from one to four feet in 
length, computed from the corrected formula: 



* The discussion of " rectangular weirs," "Cipolletti weirs'' and "90-degree 
triangular notch weirs," together with the discharge tables for these weir 
notches, is copied largely from Farmers' Bulletin No. 813, entitled "Construc- 
tion and Use of Farm Weirs, ' ' by Victor M. Cone. 



UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION 

TABLE 1 

Discharge Table for Rectangular Weirs 







Discharge in 


cubic feet per second 






Discharge in 


cubic feet per second 


Head 


Head 


for crests of various lengths 


Head 


Head 


for crests of various lengths 


in 


in 










in 


in 












feet 


inches 












feet 


inches 
















lfoot 


1.5 feet 


2 feet 


3 feet 


4 feet 






lfoot 


1.5 feet 


2 feet 


3 feet 


4 feet 


0.20 


2% 


0.291 


0.439 


0.588 


0.887 


1.19 


.86 


10ft « 


2.46 


3.72 


5.01 


7.59 


10.19 


.21 


2*4 


.312 


.472 


.632 


.954 


1.28% 


.87 


10ft 6 


2.50 


3.79 


5.10 


7.72 


10.36 


.22 


2% 


.335 


.505 


.677 


1.02 


1.37 


.88 


10ft 6 


2.54 


3.85 


5.18 


7.85 


10.54 


.23 


2% 


.358 


.539 


.723 


1.09 


1.46 


.89 


lOlfte 


2.58 


3.92 


5.27 


7.99 


10.71 


.24 


2% 


.380 


.574 


.769 


1.16 


1.55 


.90 


lOHie 


2.62 


3.98 


5.35 


8.12 


10.89 


.25 


3 


.404 


.609 


.817 


1.23 


1.65 


.91 


lOHis 


2.67 


4.05 


5.44 


8.25 


11.07 


.26 


3« 


.428 


.646 


.865 


1.31 


1.75 


.92 


Il*'l6 


2.71 


4.11 


5.53 


8.38 


11.25 


.27 


3% 


.452 


.682 


.914 


1.38 


1.85 


.93 


lifts 


2.75 


4.18 


5.62 


8.52 


11.43 


.28 


3% 


.477 


.720 


.965 


1.46 


1.95 


.94 


11*4 


2.79 


4.24 


5.71 


8.65 


11.61 


.29 


3*4 


.502 


.758 


1.02 


1.53 


2.05 


.95 


11% 


2.84 


4.31 


5.80 


8.79 


11.79 


.30 


3% 


.527 


.796 


1.07 


1.61 


2.16 


.96 


11*4 


2.88 


4.37 


5.89 


8.93 


11.98 


.31 


3% 


.553 


.836 


1.12 


1.69 


2.26 


.97 


11% 


2.93 


4.44 


5.98 


9.06 


12.16 


.32 


3Hi« 


.580 


.876 


1.18 


1.77 


2.37 


.98 


11% 


2.97 


4.51 


6.07 


9.20 


12.34 


.33 


3 Hi 6 


.606 


.916 


1.23 


1.86 


2.48 


.99 


11% 


3.01 


4.57 


6.15 


9.34 


12.53 


.34 


4*i 6 


.634 


.957 


1.28 


1.94 


2.60 


1.00 


12 


3.06 


4.64 


6.25 


9.48 


12.72 


.35 


4ft 6 


.661 


.999 


1.34 


2.02 


2.71 


1.01 


12*4 




4.71 


6.34 


9.62 


12.91 


.36 


4% 6 


.688 


1.04 


1.40 


2.11 


2.82 


1.02 


12ft 




4.78 


6.43 


9.76 


13.10 


.37 


4fi 6 


.717 


1.08 


1.45 


2.20 


2.94 


1.03 


12% 




4.85 


6.52 


9.90 


13.28 


.38 


4ft 6 


.745 


1.13 


1.51 


2.28 


3.06 


1.04 


12*4 




4.92 


6.62 


10.04 


13.47 


.39 


4 Hi 6 


.774 


1.17 


1.57 


2.37 


3.18 


1.05 


12% 




4.98 


6.71 


10.18 


13.66 


.40 


4i?i 6 


.804 


1.21 


1.63 


2.46 


3.30 


1.06 


12% 




5.05 


6.80 


10.32 


13.85 


.41 


41% 8 

5*i 6 


.833 
.863 


1.26 
1.30 


1.69 
1.75 


2.55 
2.65 


3.42 
3.54 


1.07 
1.08 


12Hie 
12Hi 6 




5.12 
5.20 


6.90 
6.99 


10.46 
10.61 


14 04 


.42 




14.24 


.43 


5?i 6 


.893 


1.35 


1.81 


2.74 


3.67 


1.09 


13*i 6 




5.26 


7.09 


10.75 


14.43 


.44 


5*i 
5% 
5*4 
5% 
5% 
5% 
6 


.924 
.955 
.986 
1.02 
1.05 
1.08 
1.11 


1.40 
1.44 
1.49 
1.54 
1.59 
1.64 
1.68 


1.88 
1.94 
2.00 
2.07 
2.13 
2.20 
2.26 


2.83 
2.93 
3.03 
3.12 
3.22 
3.32 
3.42 


3.80 
3.93 
4.05 
4.18 
4.32 
4.45 
4.58 


1.10 
1.11 
1.12 
1.13 
1.14 
1.15 
1.16 


13ft 6 
13ft 6 

13ft 6 

13ft 6 
13 Hi e 
13Hie 
13 Hi e 




5.34 
5.41 
5.48 
5.55 
5.62 
5.69 
5.77 


7.19 
7.28 
7.38 
7.47 
7.57 
7.66 
7.76 


10.90 
11.04 
11.19 
11.34 
11.48 
11.64 
11.79 


14.64 


.45 




14.83 


.46 




15.03 


.47 




15.22 


.48 




15.42 


.49 




15.62 


.50 




15.82 


.51 


6*4 
6*i 
6% 
6*4 


1.15 
1.18 
1.21 
1.25 


1.73 

1.78 
1.84 
1.89 


2.33 
2.40 
2.46 
2.53 


3.52 
3.62 
3.73 
3.83 


4.72 
4.86 
4.99 
5.13 


1.17 
1.18 
1.19 
1.20 


14*i 6 
14ft 6 
14*i 
14% 




5.84 
5.91 
5.98 
6.06 


7.86 
7.96 
8.06 
8.16 


11.94 
12.09 
12.24 
12.39 


16.02 


.52 




16.23 


.53 




16.43 


.54 




16.63 


.55 


6% 


1.28 


1.94 


2.60 


3.94 


5.27 


1.21 


14*4 




6.13 


8.26 


12.54 


16.83 


.56 


6% 


1.31 


1.99 


2.67 


4.04 


5.42 


1.22 


14% 




6.20 


8.35 


12.69 


17.03 


.57 


6 Hi 6 


1.35 


2.04 


2.74 


4.15 


5.56 


1.23 


14% 




6.28 


8.46 


12.85 


17.25 


.58 


6 Hi 6 


1.38 


2.09 


2.81 


4.26 


5.70 


1.24 


14% 




6.35 


8.56 


12.99 


17.45 


.59 


7*i 6 

7ft 6 


1.42 
1.45 


2.15 
2.20 


2.88 
2.96 


4.36 
4.47 


5.85 
6.00 


1.25 
1.26 


15 

15*4 




6.43 


8.66 


13.14 
13.30 


17.65 


.60 




17.87 


.61 


7ft 6 


1.49 


2.25 


3.03 


4.59 


6.14 


1.27 


15*4 








13.45 


18.07 


.62 


7ft 6 


1.52 


2.31 


3.10 


4.69 


6.29 


1.28 


15% 








13.61 


18.28 


.63 


7ft 6 


1.56 


2.36 


3.17 


4.81 


6.44 


1.29 


15*4 








13.77 


18.50 


.64 


7 Hi e 
7 Hi e 
7 Hi e 

8ft 6 

8ft e 


1.60 
1.63 
1.67 
1.71 
1.74 


2.42 
2.47 
2.53 
2.59 
2.64 


3.25 
3.32 
3.40 
3.47 
3.56 


4.92 
5.03 
5.15 
5.26 
5.38 


6.59 
6.75 
6.90 
7.05 
7.21 


1.30 
1.31 
1.32 
1.33 
1.34 


15% 
15% 
15 Hi e 

15Hie 

161i6 








13.93 
14.09 
14.24 
14.40 
14.56 


18.71 


.65 








18.92 


.66 








19.12 


.67 








19.34 


.68 








19.55 


.69 


8V 4 

8% 


1.78 
1.82 


2.70 
2.76 


3.63 
3.71 


5.49 
5.61 


7.36 
7.52 


1.35 
1.36 


16ft 6 
16ft 6 








14.72 
14.88 


19.77 


.70 








19.98 


.71 


8*4 


1.86 


2.81 


3.78 


5.73 


7.68 


1.37 


16ft 6 








15.04 


20.20 


.72 


8% 


1.90 


2.87 


3.86 


5.85 


7.84 


1.38 


16ft 6 








15.20 


20.42 


.73 


8% 


1.93 


2.93 


3.94 


5.97 


8.00 


1.39 


16Hi 6 








15.36 


20.64 


.74 


8% 
9 


1.97 
2.01 


2.99 
3.05 


4.02 
4.10 


6.09 
6.21 


8.17 
8.33 


1.40 
1.41 


16 Hi e 
16 Hi 6 








15.53 
15.69 


20.86 


.75 








21.08 


.76 


9*4 


2.05 


3.11 


4.18 


6.33 


8.49 


1.42 


17*i 6 








15.85 


21.29 


.77 


9*i 


2.09 


3.17 


4.26 


6.45 


8.66 


1.43 


17ft 6 








16.02 


21.52 


.78 


9% 


2.13 


3.23 


4.34 


6.58 


8.82 


1.44 


17*4 








16.19 


21.74 


79 


9*4 


2 17 


3 29 


4 42 


6 70 


8 99 


1 45 


17% 








16.34 


21.96 


80 


9% 


2 21 


3 35 


4 51 


6 83 


9 16 


1.46 


17*4 








16.51 


22.18 


.81 


9% 


2.25 


3.41 


4.59 


6.95 


9.33 


1.47 


17% 








16.68 


22.41 


.82 


9 HI e 


2.29 


3.47 


4.67 


7.08 


9.50 


1.48 


17% 








16.85 


22.64 


83 


9 Hi s 


2 33 


3 54 


4 75 


7 21 


9 67 


1 49 


17% 








17.01 


22.85 


.84 


10*i « 


2.37 


3.60 


4.84 


7.33 


9.84 


1.50 


18 








17.17 


23.08 


.85 


10ft. 


2.41 


3.66 


4.92 


7.46 


10.01 

















Circular 250] 



MEASUREMENT OF IRRIGATION WATER 



CIPOLLETTI WELES 

This type of weir is trapezoidal in shape, the name "Cipolletti" 
being that of the Italian engineer who proposed its use. As shown 
in figure 3, the crest of the weir, or bottom of the weir notch, must 
be level, and the sides placed on a slope of one to four, meaning one 
unit horizontal to four units vertical. The notch therefore is larger 
than a rectangle with the same crest length. 

It is readily seen that the Cipolletti type of weir, or in fact any 
weir having sloping sides, is not so easy either to construct or to 
check for accurracy as is the rectangular weir. The great popular- 
ity of the Cipolletti weir is due somewhat to its having been proposed 



1 , ~>r>l/" ~l 


r% 


T L 


24*-$$$ J 


^ Yfe^Tf-r . 7T^1 L 


K J> 



Fig. 3. Two foot Cipolletti weir notch. 



at a time when the use of weirs for measuring irrigation water was 
being considered, but principally because the angle which the sides 
make with the crest was supposed to make the flow over the weir 
proportional to the length of the crest. In other words, the flow for 
a certain head on a two-foot weir was supposed to be twice the flow 
over a one-foot weir for the same depth of water, which would re- 
quire but a simple weir table for field use. Recent experiments, 
however, prove that the flow over Cipolletti weirs is not proportional 
to the length of the crest, which apparently refutes the principal 
argument in its favor. However, if the sides are placed properly 
with respect to the crest, and other conditions are observed fully, 
the flow can be measured as accurately over a Cipolletti weir as over 
a rectangular weir, by use of the accompanying weir tables, or formula. 
It is all right, therefore, to use a Cipolletti weir if built properly, but 
where a weir is to be constructed, the rectangular should be chosen in 
preference to the Cipolletti type. Table 2 gives the discharge over 
Cipolletti weirs from one to four feet in length, computed from the 
corrected formula. 



10 



UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 



TABLE 2 

Discharge Table for Cipolletti Weirs 



Head 

in 
inches 



Discharge in cubic feet per second 
for crests of various lengths 



2% 
2*4 
2% 
231 
2% 
3 

3% 
3% 
3*4 
3% 
3% 

31?'l6 
3 15 'l6 

4*ie 

43'i6 
49l6 
4?16 

4%e 
4Hie 
4i?i6 

41%6 

5*ie 
59ie 
5% 
5% 
5*4 
5% 
5% 
5% 
6 

6*4 
6% 
614 
6% 
6% 

6^16 

6^16 
71'l6 
7%6 
79'l6 
7 7 /l6 

791e 
7H'i6 
7i?i 6 

71%6 
8116 

89ie 

8*4 

8% 

814 

8% 

8% 

8% 

9 

914 

914 

994 

914 

9% 

9% 

9»9'l6 
9^16 

1011s 

109*6 



1 foot 1.5 feet 2 feet 



0.30 

.32 

.35 

.37 

.39 

.42 

.45 

.47 

.50 

.53 

.56 

.59 

.61 

.64 

.67 

.70 

.73 

.77 

.80 

.83 

.87 

.90 

.93 

.97 

1.00 

1.04 

1.07 

1.11 

1.15 

1.18 

1.22 

1.26 

1.30 

1.34 

1.38 

1.42 

1.46 

1.50 

1.54 

1.58 



1 

1 

1 

1 

1 

1 

1.89 

1.93 

1.98 

2.02 

2.07 

2.12 

2.16 

2.21 

2.26 

2.31 

2.36 

2.41 

2.46 

2.51 

2.56 

2.61 

2.66 

2.71 

2.77 

2.82 



0.45 
.48 
.52 
.55 
.59 
.63 
.67 
.70 
..74 
.79 
.83 
.87 
.91 
.95 
1.00 
1.04 
1.09 
1.13 
.1.18 
1.23 
1.28 
1.32 
1.37 
1.42 
1.47 
1.53 
1.58 
1.63 
1.68 
1.74 
1.79 
1.85 
1.90 
1.96 
2.02 
2.07 
2.13 
2.19 
2.25 
2.31 
2.37 
2.43 
2.49 
2.55 
2.62 
2.68 
2.75 
2.81 
2.87 
2.94 
3.01 
3.07 
3.14 
3.21 
3.28 
3.35 
3.42 
3.49 
3.56 
3.63 
3.70 
3.77 
3.84 
3.92 
3.99 
4.07 



0.60 

.64 

.69 

.74 

.79 

.84 

.89 

.94 

.99 

1.04 

1.10 

1.15 

1.21 

1.27 

1.32 

1.38 

1.44 

1.50 

1.57 

1.63 

1.69 

1.76 

1.82 

1.89 

1.95 

2.02 

2.09 

2.16 

2.23 

2.30 

2.37 

2.44 

2.51 

2.59 

2.66 

2.74 

2.81 

2.89 

2.97 

05 



13 

20 

28 

■il 

45 

53 

61 

3.70 

3.79 

3.87 

3.95 

4.04 

4.13 

4.22 

4.31 

4.40 

4.49 

4.58 

4.67 

4.76 

4.85 

4.95 

5.04 

5.14 

5.23 

5.33 



3 feet 



0.90 
.97 
1.04 
1.11 
1.18 
1.25 
1.33 
1.40 
1.48 
1.56 
1.64 
1.73 
1.80 
1.89 
1.98 
2.07 
2.16 
2.25 
2.34 
2.43 
2.53 
2.62 
2.72 
2.81 
2.91 
3.01 
3.11 
3.21 
3.32 
3.42 
3.53 
3.64 
3.74 
3.85 
3.96 
4.07 
4.18 
4.30 
4.41 
4.53 
4.64 
4.76 
4.88 
5.00 
5.12 
5.24 
5.36 
5.48 
5.61 
5.73 
5.86 
5.99 
6.12 
6.24 
6.38 
6.51 
6.64 
6.77 
6.90 
7.04 
7.18 
7.31 
7.45 
7.59 
7.73 
7.87 



4 feet 



1.20 
1.29 
1.38 
1.47 
1.57 
1.67 
1.77 
1.87 
1.97 
2.08 
2.19 
2.30 
2.41 
2.52 
2.64 
2.75 
2.87 
2.99 
3.11 
3.24 
3.36 
3.49 
3.61 



74 
.87 
.01 

14 
.28 
.41 

55 



3. 

3. 
4. 
4. 
4. 
4. 
4. 
4.69 
4.83 
4.97 
5.12 
5.26 
5.41 
5.56 
5.71 
5.86 
6.01 
6.17 
6.32 
6.47 
6.63 
6.79 
6.95 
7.11 
7.28 
7.44 
7.61 
7.77 
7.94 
8.11 
8.28 
8.45 
8.62 
8.80 
8.97 
9.15 
9.33 
9.51 
9.69 
9.87 
10.05 
10.23 
10.42 



Head 
in 

feet 



.86 

.87 

.88 

.89 

.90 

.91 

.92 

.93 

.94 

.95 

.96 

.97 

.98 

.99 

1.00 

1.01 

1.02 

1.03 

1.04 

1.05 

1.06 

1.07 

1.08 

1.09 

1.10 

1.11 

1.12 

1.13 

1.14 

1.15 

1.16 

1.17 

1.18 

1.19 

1.20 

1.21 

1.22 

1.23 

1.24 

1.25 

1.26 

1.27 

1.28 

1.29 

1.30 

1.31 

1.32 

1.33 

1.34 

1.35 

1.36 

1.37 

1.38 

1.39 

1.40 

1.41 

1.42 

1.43 

1.44 

1.45 

1.46 

1.47 

1.48 

1.49 

1.50 



Head 
nches 



lCYie 

10%6 

lOTie 
lOHle 
10'% 6 

ioiy 16 

lllie 

11316 

1111 

U% 

11*4 

11% 

1194 

11% 

12 

12H 

1214 

1294 

1214 

12% 

1294 

1219! e 

1219'ie 

1311c 

13916 

13916 

13?16 

139ie 
13H' 16 
131916 

13^16 

14*16 

149.6 

1414 

14% 

1414 

14% 

1494 

14% 

15 

1514 

1514 

1594 

1514 

15% 

1594 

151916 

15^16 
16116 

16916 
1691e 
16?i 8 
169ie 
16H16 
16*946 

16^16 

17*1 6 

17916 
17*4 
17% 
17*4 
17% 
1794 
17% 
18 



Discharge in cubic feet per second 
for crests of various lengths 



lfoot 1.5 feet 2 feet 3 feet 4 feet 



2.87 
2.93 
2. 98 
3.04 
3.09 
3.15 
3.20 
3.26 
3.32 
3.37 
3.43 
3.49 
3.55 
3.61 
3.67 



4.14 
4.22 
4.29 
4.37 
4.45 
4.53 
4.60 
4.68 
4.76 
4.84 
4.92 
5.00 
5.09 
5.17 
5.25 
5.33 
5.42 
5.50 
5.59 
5.67 
5.76 
5.84 
5.93 
6.02 
6.11 
6.20 
6.29 
6.37 
6.46 
6.56 
6.65 
6.74 
6.83 
6.93 
7.02 
7.11 
7.20 
7.30 
7.40 
7.49 



5.43 
5.52 
5.62 
5.72 
5.82 
5.92 
6.02 
6.13 
6.23 
6.33 
6.44 
6.55 
6.64 
6.75 
6.86 
6.96 
7.07 
7.18 
7.29 
7.40 
7.51 
7.62 
7.73 
7.84 
7.96 
8.07 
8.18 
8.29 
8.41 
8.53 
8.65 
8.76 
8.88 
9.10 
9.12 
9.24 
9.36 
9.48 
9.60 
9.72 



8.01 
8.15 
8.30 
8.44 
8.59 
8.73 
8.88 
9.03 
9.17 
9.32 
9.48 
9.62 
9.78 
9.93 
10.08 
10.24 
10.40 
10.55 
10.71 
10.87 
11.03 
11.18 
11.35 
11.51 
11.68 
11.84 
12.00 
12.16 
12.33 
12.50 
12.67 
12.84 
13.01 
13.18 
13.35 
13.52 
13.69 
13.87 
14.04 
14.21 
14.39 
14.56 
14.74 
14.92 
15.11 
15.29 
15.46 
15.64 
15.82 
16.01 
16.19 
16.37 
16.57 
16.75 
16.94 
17.13 
17.31 
17.51 
17.70 
17.89 
18.08 
18.28 
18.47 
18.66 
18.85 



10.60 
10.79 
10.98 
11.17 
11.36 
11.55 
11.74 
11.94 
12.13 
12.33 
12.53 
12.72 
12.92 
13.12 
13.32 
13.53 
13 . 73 
13.94 
14.15 
14.35 
14.56 
14.76 
14.98 
15.19 
15.41 
15.62 
15.84 
16.04 
16.26 
16.48 
16.70 
16.93 
17.15 
17.37 
17.59 
17.81 
18.03 
18.27 
18.49 
18.71 
18.95 
19.17 
19.41 
19.65 
19.88 
20.12 
20.34 
20.58 
20.82 
21.06 
21.29 
21.53 
21.78 
22.02 
22.27 
22.51 
22.75 
23.01 
23.26 
23.50 
23.75 
24.01 
24.26 
24.50 
24.75 



Circular 250] 



MEASUREMENT OF IRRIGATION WATER 



11 



90-DEGEEE TEIANGULAE-NOTCH WEIRS 

This type of weir (Fig. 4) deserves to be more widely used than 
at present for the measurement of small quantities of water to the 
irrigator. If sufficient fall is available it may be used for flows as 
great as fourteen second-feet, which would be obtained with a depth 
of practically two feet of water above the vertex, or lowest point, of 
the angle formed by the sides. However, conditions usually are not 
favorable for its use for such large heads, and table 3 gives the 
discharge for heads up to 1.25 feet. Since the sides meet at a point 
with no length of crest, a small flow of water that would not pass 
over one of the other weirs without adhering to the crest and therefore 
making the measurement worthless, will flow free in the ninety-degree 




Fig. 4. 90° weir notch. 



triangular notch and may be measured accurately. The ninety-degree 
triangular notch is especially applicable from small flows up to two 
or three cubic feet per second. Because of the greater depth of water 
required for this type of weir to discharge a given quantity of water, 
and the consequent greater loss of head, one of the other types of weirs 
usually will be better adapted to large quantities of water. Experi- 
ments have shown that the rectangular and Cipolletti weirs with six- 
inch crest lengths do not follow the same laws of discharge as the 
longer weirs, and the discharge formulae given in this circular for 
these weirs do not apply to weirs with a crest length of six inches or 
less. Therefore, where only a small flow of water is to be measured 
the use of the ninety-degree triangular notch is especially recom- 
mended. 

The sides of the ninety-degree triangular notch may be set read- 
ily by means of a carpenter's square and level. The notch can be 
marked out properly by placing the point of the angle between the 
arms of a carpenter's square at a point which is to be the bottom 
of the notch and adjusting the square so that the same figures on 



12 



UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION 



both arms of the square are at the edge of the board, then if the 
board is set level the notch will be in the proper position. The sides, 
therefore, have the same slope. 

Table 3 gives the discharge over the ninety-degree triangular 
notch, computed from the corrected formula: 

TABLE 3 

Discharge Table for 90° Triangular Notch 







Discharge 






Discharge 






Discharge 


Head in 


Head in 


in second- 


Head in 


Head in 


in second- 


Head in 


Head in 


in second- 


feet 


inches 


feet (Q) 


feet 


inches 


feet (Q) 


feet 


inches 


feet (Q) 


0.20 


2% 


0.046 


0.55 


6% 


0.564 


0.90 


101?'l6 


1.92 


.21 


2*4 


.052 


.56 


6% 


.590 


.91 


ioiy, 6 


1.97 


.22 


2% 


.058 


.57 


6^8 


.617 


.92 


lUie 


2.02 


.23 


2% 


.065 


.58 


m* 


.644 


.93 


11%6 


2.08 


.24 


2% 


.072 


.59 . 


7Via 


.672 


.94 


11% 


2.13 


.25 


3 


.080 


.60 


7%6 


.700 


.95 


11% 


2.19 


.26 


3% 


.088 


.61 


7%a 


.730 


.96 


n% 


2.25 


.27 


3% 


.096 


.62 


7yi 6 


.760 


.97 


n% 


2.31 


.28 


3% 


.106 


.63 


7%6 


.790 


.98 


n% 


2.37 


.29 


3*4 


.115 


.64 


7Hi 6 


.822 


.99 


n% 


2.43 


.30 


3% 


.125 


.65 


7Mia 


.854 


1.00 


12 


2.49 


.31 


3% 


.136 


.66 


7Hia 


.887 


1.01 


12% 


2.55 


.32 


3i?ic 


.147 


.67 


8Vi 6 


.921 


1.02 


12% 


2.61 


.33 


3^16 


.159 


.68 


8%8 


.955 


1.03 


12% 


2.68 


.34 


4H« 


.171 


.69 


8*4 


.991 


1.04 


12% 


2.74 


.35 


4%6 


.184 


.70 


8% 


1.03 


1.05 


12% 


2.81 


.36 


4<j'l6 


.197 


.71 


8tf 


1.06 


1.06 


12% 


2.87 


.37 


4%a 


.211 


.72 


8% 


1.10 


1.07 


12i% 6 


2.94 


.38 


4?i 6 


.226 


.73 


8% 


1.14 


1.08 


12i% 6 


3.01 


.39 


4Hie 


.240 


.74 


8% 


1.18 


1.09 


13%6 


3.08 


.40 


4% 


.256 


.75 


9 


1.22 


1.10 


13%6 


3.15 


.41 


4% 


.272 


.76 


9tf 


1.26 


1.11 


13%6 


3.22 


.42 


5Vie 


.289 


.77 


9% 


1.30 


1.12 


13%6 


3.30 


.43 


5«a 


.306 


.78 


9% 


1.34 


1.13 


13%6 


3.37 


.44 


5% 


.324 


.79 


9*4 


1.39 


1.14 


131%6 


3.44 


.45 


5% 


.343 


.80 


9% 


1.43 


1.15 


13Mi6 


3.52 


.46 


5% 


.362 


.81 


9% 


1.48 


1.16 


13i% 6 


3.59 


.47 


5% 


.382 


.82 


99ia 


1.52 


1.17 


14Ko 


3.67 


.48 


5% 


.403 


.83 


9*%6 


1.57 


1.18 


14%6 


3.75 


.49 


5% 


.424 


.84 


10*ia 


1.61 


1.19 


14% 


3.83 


.50 


6 


.445 


.85 


10?ia 


1.66 


1.20 


14% 


3.91 


.51 


6% 


.468 


.86 


10%a 


1.71 


1.21 


14% 


3.99 


.52 


6*4 


.491 


.87 


10'/l6 


1.76 


1.22 


14% 


4.07 


.53 


6% 


.515 


.88 


1015a 


1.81 


1.23 


14% 


4.16 


.54 


6% 


.539 


.89 


lOHis 


1.86 


1.24 
1.25 


14% 
15 


4.24 
4.33 



WEIR CONSTRUCTION 

The type of the soil in which a weir is to be placed is important 
in determining whether a simple weir board or a more elaborate 
weir box should be used. In heavy clay soils where excessive wash- 
ing of the soil does not occur, a simple bulkhead placed across the 
stream can be used. In lighter soils where the washing out of ditch 
structures is liable to occur, a weir box is necessary. 

Figure 5 is an isometric drawing of a simple weir bulkhead which 
can be easily constructed on the farm. Table 4 gives the sizes of 



Circular 250] 



MEASUREMENT OF IRRIGATION WATER 



13 



weirs and weir bulkheads best adapted for the measuring of heads 
of water from one-half cubic foot per second to thirteen cubic feet 
per second. The letters at the heads of the columns refer to the 
dimensions as shown in figure 5 : 



"*^^ 




' r-% "\s4M& 




J\ 


f 




^T^***^'- r-a . 


ior/tJ'i^' 








■% / 


si » 


"* H *" 


C 




1 

_ _G 






"1 






/ 








/ 




< 


D 








K 


U 











Fig. 5. Isometric drawing of weir bulkhead. Suitable only for rather heavy soil. 



TABLE 4 
Weir Board Dimensions tor Rectangular and Cipolletti Weirs 
Letters at head of columns refer to figure 5. 













Total 


Distance 




Distance of 


Capacity 




Maximum 




Total 


length of 


of crest, 




edge of 


of weir, 


Length 


head over 


Depth 


depth of 


bulk- 


G, above 


Length 


notch, F, 


cubic feet 


of crest, 


weir crest, 


of notch, 


bulkhead 


head, 


ditch 


of wing, 


from ditch 


per second 


A, feet 


B, feet 


H, feet 


C, feet 


D, feet 


bottom, ft. 


E, feet 


bank, feet 


Hto2 


1.5 


.56 


1.0 


3.0 


10.0 


0.3 


4.25 


1.5 


1 to 7V 2 


3.0 


.86 


1.0 


4.0 


12.0 


0.5 


4.50 


2.0 


\Yt to 13 


4.0 


1.00 


1.5 


5.0 


16.0 


0.7 


6.00 


2.5 



With rectangular or Cipolletti weirs, as previously stated, the 
head of water can best be measured from a stake driven in the ditch 
bank or bottom to the elevation of the weir crest and about three 
feet upstream from the crest. The stake can be easily set with an 
accurate carpenter's level. The depth of water over this stake, as 
shown by a carpenter's rule, will then measure the depth of water 
passing over the weir. 

Figure 6 shows the construction of a complete weir box. The 
letters refer to table 5, which shows the dimensions of these boxes as 
built for measuring heads of water from one-half cubic foot per 
second to seventeen cubic feet per second: 



14 



UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 



TABLE 5 

Dimensions for Weir Boxes as Shown in Figure 6 
Letters at head of columns refer to figure 6. 























Distance 






















of crest 






Maxi- 


Total 


Total 


Total 


Distance 




Edge of 




above 


Capacity 




mum 


depth 


depth 


length 


of crest 




notch, 


Distance 


overflow 


of weir, 


Length 


head 


of 


of 


of 


above 


Length 


F, from 


between 


of 


cubic 


of 


over 


notch, 


bulk- 


bulk- 


ditch 


of 


ditch 


bulk- 


water 


feet per 


crest, 


weir, 


H, 


head, 


head, 


bottom, 


wing, 


bank, 


heads, 


cushion, 


second 


A, feet 


B, feet 


feet 


C, feet 


D, feet 


G, feet 


E, feet 


feet 


I, feet 


M, feet 


Hto2H 


1.5 


.67 


1.0 


3.0 


10.0 


0.3 


4.25 


1.5 


3.0 


1.0 


2 to 7V 2 


3.0 


.86 


1.0 


4.0 


12.0 


0.5 


4.50 


2.0 


3.0 


1.2 


6 to 17 


4.0 


1.20 


1.5 


5.0 


16.0 


0.7 


6.00 


2.5 


3.5 


1.4 



Note. — In all cases assumed in figure 6 the water cushion below the weir crest is 6 inches deep, 
although any depth that will give sufficient pool to break the fall of the water, in order to prevent 
ditch erosion below, is satisfactory. The overflow from this cushion should be on the grade of the 
ditch bottom as it leaves the structure. In the last column of the table, definite distances of crest, 
M, above the overflow of the water cushion are assumed, because these distances are ample. Any 
drop, however, that permits a free fall of the water over the weir crest meets the conditions required 
by the weir formula. 

SUBMERGED ORIFICES 

In cases where the grade of ditch is so flat that the required free 
fall over a weir can not be easily obtained, and in cases where the 
waters are so heavily charged with silt that there is danger of a 
weir pond silting up, some type of submerged orifice is commonly 
used. 

The measurement of water through orifices has long been com- 
mon in irrigation practice and various forms of orifices have been 




Fig. 6. Isometric drawing of weir bulkhead. Designed for light soils. 



Circular 250] 



MEASUREMENT OF IRRIGATION WATER 



15 



developed. The essential condition in the use of an orifice, eliminat- 
ing the question of form, is that the water on the up-stream side of 
the orifice shall completely submerge it. If, when in use, the surface 
of the water on the lower side of the orifice is below the bottom 
thereof, the orifice is said to have a free discharge. If the surface 
of the water on the lower side of the orifice is above the top of the 



rCaRPENTdR's RULE Caf?PENT£R'S^R(JLEp 


^x 


1 


_1_ 

"h" 


: 




^d 


\ 


- 




^~ 


. ^- 




Y ?' I 


. 


.— , 


r J 1 


* 3 ■ H 


t 1 




4 


i ' ' 
Sr/7/f/r -^J, \ 


ij 



Fig. 7. Diagrammatic sketch showing orifice of fixed dimensions in use. 




Tig. 8. Isometric drawing of U.S.R.S. submerged orifice. 



16 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 

orifice, completely submerging it, it is classed as a submerged ori- 
fice. Except in the case of the miner's inch box, which is really 
but a form of orifice with free discharge, use of the orifice in irri- 
gation practice is mainly confined in California to the submerged 
form. 

Submerged orifices as used can be divided into two general types, 
viz: those with orifices of fixed dimensions (Fig. 8) and those built 
so that the height of the opening may be varied (Figs. 9 and 10). 




Fig. 9. Photograph of adjustable submerged orifice in use. 

Orifices of fixed dimensions are usually made with sharp edges simi- 
lar to the crest of a weir. The most usual type of adjustable ori- 
fice is the simple head gate, the height of opening and loss of head 
being adjusted to the amount which it is desired to turn out and 
to the loss of head available. Of these two types, the sharp-edged 
orifice of fixed dimensions is much the more accurate in practice. 

With either of these types of submerged orifice, the quantity of 
water passing through the orifice is measured by the difference in 
water level above and below the orifice. Such a difference in water 
level always exists in devices of this sort. This difference in water 
level is commonly called the "difference in head" or "loss of head." 
A small "la" is usually used to represent this difference. 

Figure 7 is a diagramatic sketch of a submerged orifice in use. 

The amount of water which passes through a submerged orifice 
of fixed dimensions increases as "h" increases. Theoretically, if 



Circular 250] 



MEASUREMENT OF IRRIGATION WATER 



17 



"h" could be indefinitely increased, any quantity of water could be 
passed through an orifice with an area of one square foot. Practical 
difficulties make it impossible for this difference in head in small 
ditches ever to become larger than about eighteen inches. In ditches 
on very flat grades this difference in head can not become more than 
four or five inches without endangering the ditch bank above the 
orifice. 




Fig. 10. Isometric drawing of adjustable submerged orifice. 



In cases where sufficient discharge can not be obtained through 
the orifice with the loss in head that is permissible, a larger orifice 
may be used. With a given difference in head, the discharge is 
directly proportional to the area of the orifice and unreasonable dif- / 
ference in head can be reduced by increasing this area.* 



* With crude adjustable submerged orifices, the statement that the discharge 
for a given loss of head is directly proportional to the area of the orifice is not 
strictly true. Work done by the Kern County Land Company shows that the 
value of "C" in the formula v=C \/2g~h varies with changes in the area of 
the opening. The exact proportion is consequently destroyed. 



18 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 



SUBMEEGED OKIFICE WITH FIXED DIMENSIONS 

This type of submerged orifice is used for measurements only, 
the fixing of the size of the opening preventing its use as a headgate. 

In order that the known formulae for the discharge through such 
orifices shall apply, certain standard conditions must be observed in 
their construction and use. The edges of the orifice must be sharp 
and definite in shape. It is preferable to use a thin metal plate as 
this is not subject to wear and change. The edges of the orifice 
should not be too near to the sides of the box on either the upper or 
lower sides; a distance equal to twice the least dimension of the ori- 
fice is sufficient. The sides of the orifice should be vertical and the 
bottom edge level. The ditch above the orifice should be sufficiently 
large so that the velocity of approach will be small, as is necessary 
in the case of a weir. Corrections can be made in the computations 
for any velocity of approach but such corrections are more or less 
uncertain. 

The principal sources of error in measurements with this type 
of orifice are due to errors in the gauge readings to determine the 
difference in the elevation of the water on the two sides, this being 
the head or pressure that forces the water through the orifice. As 
these orifices are generally used where there is but little loss of head 
available, the opening is usually made sufficiently large to require 
as little loss of head as is practicable. Any error in reading this 
small loss of head is thus a larger percentage of the whole than it 
would be for greater total differences. 

In the use of the submerged orifice two gauge readings are re- 
quired, one above and one below the orifice. The reading above the 
orifice should be taken back from the edge of the orifice. In the type 
of structure shown in figures 8 and 10 this can be taken on the side 
wing wall. Perhaps a still better way is to drive two stakes in the 
bottom of the ditch, one of which should be about three feet above 
the orifice and the other three feet below. By driving these stakes 
to the same elevation and measuring the depth of water over each 
of them, the difference in head or "h" can be easily determined. 
This quantity is, of course, the difference between these two depths. 

The type of orifice described above and illustrated in figure 8 
has been adopted by the United States Reclamation Service for use 
where sufficient loss of head is not available for weirs. The data 
given below regarding the sizes of the structures, and the table of 
discharges (table 6) are taken from the publication of the Reclama- 
tion Service on the measurement of irrigation water and from their 



Circular 250] 



MEASUREMENT OF IRRIGATION WATER 



19 



standard plans for submerged orifices. The cost of one of these de- 
vices installed will vary from about $10 to $30. 



TABLE 6 

Discharge of Submerged Eectangular Orifices in Cubic Feet per Second 

Taken from il Hydraulic and Excavation Tables' ' published by the 

U. S. Eeclamation Service 



Head h, 


Head h, 
feet 




Cross-sectional area A of orifice 


, square feet 




inches 






















0.25 


0.5 


0.75 


1.0 


1.25 


1.5 


1.75 


2.0 


ft 


0.01 


0.122 


0.245 


0.367 


0.489 


0.611 


0.734 


0.856 


0.978 


ft 


.02 


0.173 


0.346 


0.518 


0.691 


0.864 


1.037 


1.210 


1.382 


ft 


.03 


0.212 


0.424 


0.635 


0.847 


1.059 


1.271 


1.483 


1.694 


ft 


.04 


0.245 


0.489 


0.734 


0.978 


1.223 


1.468 


1.712 


1.957 


ft 


.05 


0.273 


0.547 


0.820 


1.093 


1.367 


1.640 


1.913 


2.186 


ft 


.06 


0.300 


0.599 


0.899 


1.198 


1.497 


1.797 


2.097 


2.396 


»ft« 


.07 


0.324 


0.647 


0.971 


1.294 


1.617 


1.941 


2 . 265 


2.588 


«Ka 


.08 


0.346 


0.691 


1.037 


1.383 


1.729 


2.074 


2.420 


2.766 


1«6 


.09 


0.367 


0.734 


1.101 


1.468 


1.835 


2.201 


2 638 


2.935 


lft« 


.10 


0.387 


0.773 


1.160 


1.557 


1.933 


2.320 


2.707 


3.094 


lfts 


.11 


0.406 


0.811 


1.217 


1.622 


2.027 


2.433 


2.839 


3.244 


lgi 


.12 


0.424 


0.847 


1.271 


1.694 


2.118 


2.542 


2.965 


3.389 


1«16 


.13 


0.441 


0.882 


1.323 


1.764 


2.205 


2.645 


3.086 


3.527 


1% 


.14 


0.458 


0.915 


1.373 


1.830 


2.287 


2.745 


3.203 


3.660 


1^6 


.15 


0.474 


0.947 


1.421 


1.895 


2.369 


2.842 


3.316 


3.790 


l*Si« 


.16 


0.489 


0.978 


1.467 


1.956 


2.445 


2.934 


3.423 


3.912 


2fte 


.17 


. 504 


1.008 


1.512 


2.016 


2.520 


3.024 


3.528 


4.032 


2ft« 


.18 


0.519 


1.037 


1.556 


2.075 


2.593 


3.112 


3.631 


4.150 


2% 


.19 


0.533 


1.066 


1.599 


2.132 


2.665 


3.198 


3.731 


4.264 


2% 


.20 


0.547 


1.094 


1.641 


2.188 


2.735 


3.282 


3.829 


4.376 


2ft 


.21 


0.561 


1.120 


1.681 


2.241 


2.801 


3.361 


3.921 


4.482 


2% 


.22 


0.574 


1.148 


1.722 


2.926 


2.870 


3.464 


4.018 


4.592 


2% 


.23 


0.587 


1.172 


1.759 


2.345 


2.931 


3.517 


4.103 


4.690 


2% 


.24 


0.600 


1.198 


1.797 


2.396 


2.995 


3.599 


4.193 


4.792 


3 


.25 


0.612 


1.223 


1.834 


2.446 


3.057 


3.668 


4.280 


4.891 


3ft 


.26 


0.624 


1.247 


1.871 


2.494 


3.117 


3.741 


4.365 


4.988 


3ft 


.27 


0.636 


1.270 


1.906 


2.541 


3.176 


3.811 


4.446 


5.082 


3% 


.28 


0.646 


1.294 


1.942 


2.589 


3.236 


3.883 


4.530 


5.178 


3ft 


.29 


0.659 


1.319 


1.978 


2.638 


3.297 


3.956 


4.616 


5.276 


3% 


.30 


0.670 


1.339 


2.009 


2.678 


3.347 


4.017 


4.687 


5.356 


3% 


.31 


0.681 


1.363 


2.045 


2.726 


3.407 


4.089 


4.771 


5.452 


3i?i 6 


.32 


0.692 


1.382 


2.073 


2.764 


3.455 


4.146 


4.837 


5.528 


3%i 


.33 


0.703 


1.405 


2.107 


2.810 


3.513 


4.215 


4.917 


5.620 


4fte 


.34 


0.713 


1.426 


2.139 


2.852 


3.565 


4.278 


4.991 


5.704 


4% e 


.35 


0.724 


1.446 


2.169 


2.892 


3.615 


4.338 


5.061 


5.784 


4y l6 


.36 


0.734 


1.467 


2.201 


2.934 


3.667 


4.401 


5.135 


5.868 


4%a 


.37 


0.745 


1.488 


2.232 


2.976 


3.720 


4.464 


5.208 


5.952 


4?'l6 


.38 


0.754 


1.508 


2.262 


3.016 


3.770 


4.524 


5.278 


6.032 


4Hi6 


.39 


0.764 


1.527 


2.291 


3.054 


3.818 


4.582 


5.345 


6.109 


4»«6 


.40 


0.774 


1.547 


2.321 


3.094 


3.867 


4.641 


5.415 


6.188 


4^16 


.41 


0.783 


1.567 


2.350 


3.133 


3.917 


4.700 


5.483 


6.266 


5fta 


.42 


0.792 


1.585 


2.377 


3.170 


3.962 


4.754 


5.547 


6.339 


5ft« 


.43 


0.802 


1.604 


2.406 


3.208 


4.010 


4.812 


5.614 


6.416 


5ft 


.44 


0.811 


1.622 


2.433 


3.244 


4.055 


4.866 


5.677 


' 6.488 


5% 


.45 


0.820 


1.640 


2.461 


3.281 


4.101 


4.921 


5.741 


6.562 


5ft 


.46 


0.829 


1.659 


2.489 


3.318 


4.147 


4.977 


5.807 


6.636 


5% 


.47 


0.839 


1.678 


2.517 


3.356 


4.195 


5.035 


5.874 


6.713 


5% 


.48 


0.847 


1.695 


2.542 


3.389 


4.237 


5.084 


5.931 


6.778 


5% 


.49 


0.856 


1.712 


2.568 


3.424 


4.280 


5.136 


5.992 


6.848 


6 


.50 


0.865 


1.729 


2.594 


3.458 


4.323 


5.188 


6.052 


6.917 


6ft 


.51 


0.873 


1.746 


2.620 


3.493 


4.366 


5.239 


6.112 


6.986 


6ft 


.52 


0.882 


1.763 


2.645 


3.527 


4.409 


5.290 


6.172 


7.054 


6% 


.53 


0.890 


1.780 


2.670 


3.560 


4.451 


5.341 


6.231 


7.121 


6ft 


.54 


0.898 


1.797 


2.695 


3.593 


4.491 


5.390 


6.288 


7.186 


6ft 


.55 


0.907 


1.813 


2.719 


3.626 


4.533 


5.439 


6.345 


7.252 


6% 


.56 


0.915 


1.830 


2.745 


3.660 


4.575 


5.490 


6.405 


7.320 


6% 


.57 


0.923 


1.846 


2.769 


3.692 


4.615 


5 . 538 


6.461 


7.384 


6«i 6 


.58 


0.931 


1.862 


2.794 


3.725 


4.656 


5.587 


6.518 


7.450 


7ft 8 


.59 


0.939 


1.879 


2.818 


3.757 


4.697 


5.636 


6.575 


7.514 


7%« 


.60 


0.947 


1.895 


2.842 


3.790 


4.737 


5.684 


6.632 


7.579 


7*a 


.61 


0.955 


1.910 


2.865 


3.820 


4.775 


5.730 


6.685 


7.640 


7ft« 


.62 


0.963 


1.925 


2.887 


3.850 


4.812 


5.775 


6.737 


7.700 


79is 


.63 


0.971 


1.941 


2.911 


3.882 


4.853 


5.823 


6.793 


7.764 


7Hi« 


.64 


0.978 


1.956 


2.934 


3.912 


4.890 


5.868 


6.846 


7.824 


7% 


.65 


0.986 


1.972 


2.958 


3.944 


4.930 


5.916 


6.902 


7.888 



20 



UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION 



CONSTBUCTION OF SUBMEKGED OEIFICES OF FIXED DIMENSIONS 

Figure 8 is an isometric drawing of the type of submerged orifice 
in use on many of the United States Reclamation Service projects. 
Particular attention is called to the box below the orifice into which 
the water flows as it passes through the opening. Such construction 
adds strength to the structure, minimizes the danger of its washing 
out and lessens erosion below it. 

Since structures of this sort must be built in various sizes to 
correspond to local conditions, the dimensions on the drawing (Fig. 
8) are indicated by letters. The letters refer to table 7, which gives 
these dimensions in feet for boxes with various sizes of opening. In 
all cases, the width of the head wall must be great enough to extend 
across the ditch from the center line of the ditch bank on one side 
to the center line of the ditch bank on the other side. 

TABLE 7 

Dimensions for Standard Sizes of Submerged Eectangular Orifices 

Letters showing dimensions refer to figure 8. 



Size of Orifice 


Head- 








Total 




Bottom 
of orifice 








wall 
height, 


Box 

height, 


Structure 
length, 


Floor 
width, 


width 
of 


Length 
of wing, 


above 








ditch 


Height 


Length 


Area, 


B, feet 


J, feet 


G, feet 


D, feet 


structure 


C, feet 


bottom, 


F, feet 


E, feet 


sq. feet 










A, feet 




H, feet 


.25 


1.0 


.25 


4.5 


2.5 


3.5 


2.0 


8.0 


3.0 


.25 


.25 


2.0 


.50 


4.5 


2.5 


3.5 


3.0 


10.0 


3.5 


.25 


.25 


3.0 


.75 


4.5 


2.5 


3.5 


4.0 


12.0 


4.0 


.25 


.50 


1.0 


.50 


4.5 


2.5 


3.5 


2.0 


8.0 


3.0 


.50 


.50 


1.50 


.75 


4.5 


2.5 


3.5 


2.5 


10.0 


3.75 


.50 


.50 


2.0 


1.00 


4.5 


2.5 


3.5 


3.0 


10.0 


3.5 


.50 


.50 


2.5 


1.25 


4.5 


2.5 


3.5 


3.5 


12.0 


4.25 


.50 


.50 


3.0 


1.50 


5.0 


2.5 


3.5 


4.0 


12.0 


4.0 


.50 


.75 


1.33 


1.00 


4.5 


2.5 


4.0 


2.5 


10.0 


3.75 


.70 


.75 


1.67 


1.25 


4.5 


2.5 


4.0 


3.0 


12.0 


4.5 


.70 


.75 


2.00 


1.50 


4.5 


2.5 


4.0 


3.5 


14.0 


5.25 


.70 


.75 


2.33 


1.75 


5.0 


3.0 


4.0 


3.5 


14.0 


5.25 


.70 


.75 


2.67 


2.00 


5.0 


3.0 


4.0 


4.0 


14.0 


5.0 


.70 



COMPUTATIONS IF TABLES AEE NOT AVAILABLE 

One of the advantages of the submerged orifice as a measuring de- 
vice lies in the fact that tables are not absolutely necessary for a 
ready determination of the discharge. The two basic formulae are: 

Q = AV_ 
Vr=CV2gh 
Where Q = discharge in cubic feet per second 
A = area of orifice in square feet 

V = velocity of water through opening in feet per second 
C = a coefficient which is 0.61 for a sharp-edged fixed opening 
g = acceleration of gravity or 32.16 feet per second 
h = difference in head in feet 



Circular 250] MEASUREMENT OF IRRIGATION WATER 21 

These two formulae can be combined into a single expression 

Q = AX 4.89 X Vh 

With any sharp-edged fixed orifice, the square root of the dif- 
ference in head, in feet or fractions of feet, above and below the 
orifice, multiplied by 4.89, multiplied by the area of the opening in 
square feet, will give the discharge through the opening in cubic 
feet per second. 

Example : 

Area of opening = 2 square feet 

Measured difference in head = 0.35 feet 

Discharge = 2 X 4.89 X a/0.35 = 5.78 cubic feet per second. 

ADJUSTABLE SUBMERGED OEIFICE 

A submerged orifice with a fixed opening is evidently unsuited 
to streams which are subject to wide fluctuations in discharge. For 
such conditions, a submerged orifice with an adjustable opening has 
been designed so that varying heads may be accommodated without 
endangering the banks of the canal. Such devices are in common 
use on many irrigation ditches. 

The method of measurement for the determination of the differ- 
ence in head is similar to that for the fixed orifice. In most cases 
the size of the opening can be adjusted by raising a gate which slides 
between guides nailed to the sides of the box. In such gates as this 
the size of the opening can easily be determined by calibrating the 
staff which raises the gate. A few measurements will determine how 
many square inches are added to the opening for each inch that the 
staff on the gate is raised. In many cases the adjustable gate is held 
in place by a bolt which slips through one of the holes on the staff 
of the gate and through the cross beam on the box. Since these holes 
are fixed, the hole through which the bolt passes is at once evidence 
as to the number of square inches in the opening. Labeling these 
holes with their respective openings does away with the necessity of 
repeated measurement. Figure 10 shows a gate arranged for this 
means of determining the size of the opening. 

The additional strength necessary for this adjustable gate makes it 
necessary that an adjustable submerged orifice be built in a section of 
flume or a box in place of a single wall placed across the stream. 
Figure 10 is an isometric drawing of a submerged orifice placed in a 
flume and of a size sufficient for discharges varying from one half 
cubic foot per second to twenty cubic feet per second. 



22 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION 

The accurate measurement of water through an adjustable sub- 
merged orifice can not be expected unless the individual structure has 
been rated in place. Conditions do not often permit the rating of 
orifices in the field. It has been found that variations in the structures, 
especially if built by carpenters with different degrees of skill, the 
cross section of the canal immediately above the structure, the velocity 
of the water as it approaches the structure, and the degree of sub- 
mergence of the orifice itself may all affect the discharge through the 
orifice even if the area of the opening and the difference in head may 
be constant. 

For these reasons a table of discharge for adjustable submerged 
orifices would have but little value because of the, at present, unavoid- 
able error which would be introduced. The discharge can, however, 
be quite easily computed. Such computations are sufficiently accurate 
for most purposes. 

Computation of discharge through adjustable submerged orifices. — 
The theory underlying the flow of water through adjustable orifices 
is the same as for fixed orifices. The same formulae apply : 

v = cvlTgh 

Or 



Q = ACX V2gh 
Or 

Q-AC 8.02 V h 
Where 

Q = discharge in cubic feet per second 

A = area of the orifice in square feet 

V = velocity of the stream flowing through the orifice, in feet per 
second 

C = a variable coefficient. 

g =z acceleration of gravity, 32.16 feet per second 

h = difference in head in feet. 

If the measurements of the area of the opening and the resulting 
difference in head are correctly made, the accuracy of the device 
depends upon selecting the proper value for the coefficient C for the 
existing conditions. Experiments conducted in the field laboratory at 
Davis, California, and in the hydraulic laboratory at Fort Collins, 
Colorado, suggest the use of the following values of C for various 
size of openings. If these values are used the per cent of error should 
be less than 6 per cent, unless other conditions in the individual struc- 
ture are exceptionally bad. 



CIRCULAR 250] MEASUREMENT OF IRRIGATION WATER 23 

Area of opening 
in square feet Value of C 

0.25 to 0.50 80 

0.50 to 1.95 73 

1.95 to 3.00 68 

These values of C can only be considered as trustworthy when the 
orifice is constructed according to the drawing (Fig. 10). Any change 
in the size of the posts or their location with respect to the flume would 
doubtlessly result in different side or bottom contractions. Other 
factors would then be introduced which would render these values of 
C unreliable. 

The writer would be glad to correspond with water masters and 
irrigation managers in regard to the experiments mentioned above. 



DESCBIPTION OF INCH BOX MEASUEEMENT 

A miner's inch is the amount of water which will flow through 
an opening one inch square when the center of that opening is held 
under a definite pressure. This required pressure varies in different 
localities. In most of the western states this pressure is fixed by the 
laws of the states. 

In California, although the statute specifies a pressure of six 
inches above the center of the opening, a pressure of four inches is 
in universal use in the southern part of the state. In the newer 
fruit-growing areas of the Sierra Nevada foothills the statute pres- 
sure of six inches is in common use. 

This definition of a miner's inch makes the measurement of water 
in this unit a simple matter. Many structures have been designed 
for such measurements. In these devices an adjustable opening is 
so placed that its center is exactly as many inches below a fixed 
overflow as the law or local custom prescribes. By regulating this 
adjustable opening the water above the opening can be backed up 
until the water surface stands at the exact level of the overflow. 
The average pressure on the opening is then that pressure which is 
required by the local custom, and each square inch in the opening 
delivers one miner's inch. The discharge through the opening in 
miner's inches can then be determined by measuring the opening 
and computing its area in square inches. The number of square 
inches in the opening is the number of miner's inches in the stream. 



24 



UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 



EIVEESIDE BOX 

The device used on the Riverside Canal in southern California 
is shown in use in figure 11. The water enters through the bottom 
of the box and is measured out through an adjustable cast-iron meas- 
uring plate in the end. The opening of this plate is five inches high 
and by moving the iron slide gates it can be varied in width up to 
fourteen inches. The top of the plate is four inches above the center 
of the opening. This four-inch pressure conforms to the custom in 







Fig. 11. Photograph of Riverside miner's inch box. 



southern California. Thus, if the slides are set so as to hold the 
water surface at the top of the plate, the discharge in miner's inches 
will equal the area of the opening in square inches. Marks one inch 
apart are made on the plate to assist in measuring the width. When 
the water has passed through the plate, it is usually dropped into 
a concrete pipe line and led to the point of use. Care should be 
taken in planning the installation so that the water pouring through 
the plate will have a free fall into the basin below. 

In cases where the Riverside box is used on pipe lines operating 
under considerable pressure it is often necessary that the measur- 
ing plate be installed in a standpipe several feet high. In such in- 
stallations the water pouring through the plate drops into another 



Circular 250] MEASUREMENT OF IRRIGATION WATER 25 

pipe high enough to provide the necessary pressure for the remainder 
of the line. The cost of installing a Riverside measuring plate in a 
concrete pipe line, in which the water is carried under pressure, 
varies so greatly that cost figures can not be given. 

The Riverside box shown in figure 11 is designed for delivery of 
water into open ditches or into pipe lines which require no initial 
head. Such an installation would cost about $15.00. The plate alone 
sells for $2.50. 



ANAHEIM UNION WATER COMPANY MEASURING BOX 

The measuring box of the Anaheim Union "Water Company is 
designed so that a definite amount of water can be diverted from 
the company's canal into the farmer's lateral or pipe line. The de- 
vice consists of a by-pass into which water can be diverted from 
the main canal, an adjustable miner's inch plate, and an overflow 
crest, so set that any water diverted from the main in excess of the 
quantity required pours back into the company's ditch. The meas- 
uring plate is placed so that the center line of the adjustable open- 
ing is exactly four inches below the overflow. The inaccuracies of 
the device lie in the fact that the contractions* about the opening 
are very seldom complete. These inaccuracies are all in favor of the 
water user. Figure 12 shows the measuring box of the Anaheim 
Union Water Company in use. 



* When a stream of flowing water passes over a weir having a crest length 
less than the width of the channel in which the water is flowing, the stream 
is said to have ' ' end contractions. ' ' In such cases the actual width of the stream 
of water passing over the weir is slightly less than the width of the weir, 
this being due to the curvature of the water around the sides of the weir. 
Complete end contractions for any given weir opening are reached with a 
maximum curvature of the wall and therefore with the maximum decrease 
in the width of the stream. Through numerous experiments made by hydraulic 
engineers, the distance the sides of a weir must be from the sides of the 
channel in which it is placed in order to give complete contractions have been 
determined and with any distance less than this, the contractions would be 
il incomplete' y and the quantity of water actually flowing over the weir will 
be somewhat different from that shown in the table for weirs with complete 
contractions. A weir with crest length equal to the width of the channel in 
which the weir is placed gives no end contraction or narrowing of the stream 
as it passes over the weir. Such a weir is known as a "suppressed" weir 
and different tables must be used with it. Such tables are not included in 
this circular because suppressed weirs are seldom used by farmers. 

The term "complete contractions" is also sometimes used in connection 
with weirs to denote contractions on both sides and bottom; or in the case 
of an orifice, to denote contractions on all four sides. 



26 



UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 



SANTA ANA VALLEY IRKIGATTON COMPANY'S MINER'S INCH BOX 

A somewhat different type of inch box is used by the Santa Ana 
Valley Irrigation Company, in Orange County. This is merely a 
cemented section of the lateral in which the measuring board is 
placed. Water is forced into this cemented section of the lateral by 
stop gates placed across the main ditch. The farm lateral at the 
point of measurement is uniformly 33% inches wide. The opening 




Fig. 12. The Anaheim Union Water Company's miner's inch box. 

is three inches high. If a stream of 100 miner's inches is desired, 
water is turned into the lateral until it stands four inches above the 
center of the opening in the measuring plate. If only fifty miner's 
inches are required, an opening one-half the width of the box is used. 
This opening is on one side of the lateral, however, instead of in 
the center, giving only one end contraction of the stream of water 
passing through. As a result of this, and also because there is no 
contraction on the bottom of the opening, the quantity measured 
does not correspond exactly with the amount measured through an 
opening of the same size, with contractions on all four sides. 

THE AZUSA HYDRANT 
It will be noted that the Riverside box described above can be 
used only for measuring the total flow in a ditch or pipe line. In 



Circular 250] 



MEASUREMENT OF IRRIGATION WATER 



27 



cases where the device must separate a certain flow from a larger 
stream some other method must be used. A common device of this 
sort is the Azusa hydrant. This hydrant is used exclusively on con- 




Fig. 13. Drawing of Azusa miner 's inch box. 



crete pipe lines and is usually used to separate from the water com- 
pany's supply line the amount of water ordered by individual users. 
This hydrant (Figs. 13 and 14) chiefly provides for measure- 
ment through one or more orifices on the center of which a pressure 
head of four inches is maintained by means of a sheet-iron spill crest 
set at right angles to the orifice plate. The hydrant is in the form of 
a concrete box placed over the supply pipe line. The openings in 
the orifice plate are four inches high and 2y 2 , 3%, 6%, and 12% 



28 



UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 



inches wide, giving areas of 10, 15, 25, and 50 square inches, respec- 
tively. When the water surface on the upper side of these orifices 
is held four inches above their centers they will discharge, respec- 
tively, 10, 15, 25, and 50 inches. By using different combinations of 
these orifices several different amounts up to 100 inches can be meas- 
ured. The water enters through the pipe shown in the drawing (Fig. 




> , 3&V ■ ' 



Fig. 14. Photograph of Azusa miner's inch box. Taken from above. 

13). The orifices for the desired amounts to be turned out are opened 
and the others closed with slides. By adjusting the gate under the 
spillway the water can be brought to the crest of the spillway. If 
the water rises above the spillway a large part of the excess will be 
carried back to the supply line over the spillway, but any increase 
in depth on the orifices will also increase the amount turned out. 

The Azusa hydrant as shown has walls six inches thick, all sides 
being vertical. The forms required in making it are therefore simple. 
The box contains 78.3 cubic feet of concrete. This can be made of 



Circular 250] MEASUREMENT OF IRRIGATION WATER 29 

one part cement and four parts coarse sand. As the walls are six 
inches thick it is better to add some gravel (not larger than iy 2 
inches) to the sand where this can be obtained cheaply, but the pro- 
portion of one part cement to four parts of aggregate should be 
maintained. The concrete for this box including forms will cost from 
$18.00 to $20.00 under a large contract and about $30.00 if made 
singly. The plate with the openings and slides can be bought already 
made for $12.50 from foundries in the vicinity of the places the 
hydrant is used. The gate can be any of the usual types of slide gate. 
The average of a number of tests made of this hydrant at Davis 
showed the amounts in inches being carried through the openings 
to be one per cent more than their area in square inches. This dif- 
ference includes all errors in the measurements so that these openings 
are seen to be very accurate. The tests showed all openings or com- 
binations of openings to be equally accurate. The box will there- 
fore measure as accurately as is required. The openings are not as 
closely adjustable to the amounts turned out, however, as they are 
in the case of the box of the Riverside Water Company. Errors to 
be avoided in the use of this hydrant result from allowing the water 
to pass through the openings unevenly, which produces a swirling 
motion of the water as it rises to the openings ; also from not so ad- 
justing the gate under the spill-crest as to keep the flow over the 
spill to a thin film of water. 

DIVISION BOXES 

In some places in California, as well as in other western states, 
the waters in small streams are so allotted that an individual user is 
entitled to a definite proportion of the entire flow of that stream. This 
proportion is usually fixed by consideration of the number of irri- 
gable acres each owner farms and the age of the established water 
rights. Canal companies in areas where this method of proportional 
delivery is common have at times adopted division boxes for the divi- 
sion and distribution of their supply. In such cases the company is 
commonly organized as a stock company and the stock purchased 
by the water users. One share of stock usually represents one acre 
of irrigable land. If, for instance, 100 shares of stock have been 
sold in a ditch company and one user owns ten shares, that user is 
entitled to 10/100 of the entire flow of the canal. Many types of 
division boxes have been designed in an effort to make this propor- 
tionate division just and accurate. All of these devices are based 
upon the principle that for a given head the discharge over two weir 



30 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 

crests set at the same elevation is approximately proportional to the 
length of those weir crests. 

In the example given above the water user is entitled to 10/100 
of all the water in the canal. Such a division might be made by set- 
ting two weirs at the same elevation in the canal near the farmer's 
turnout. If, for example, one of the weirs has a crest ten inches 
long and discharges its water into the farmer's lateral, and the other 
weir with a crest ninety inches long empties its water into the com- 
pany's ditch, this proportionate division would be equitably accom- 
plished, since the lengths of the weir crests would have the same 
ratio as that required by the conditions of the diversion. No matter 
how much water came down the canal, the user would receive 10/100 
of the entire flow. 

These division weirs are subject to the conditions already given 
for other weirs. These conditions are usually difficult to obtain 
throughout the length of a canal. The users at the upper end of 
the canal do not contribute toward the payment for water lost by 
seepage below them in the canal and the whole charge for this loss 
falls on the users at the lower end. 

Several structures have been designed to obviate these difficul- 
ties, but in most cases this has been done at the sacrifice of accuracy 
in the division. 

An isometric drawing of one of these devices is shown in figure 
15. With this structure the water enters the flume at the left, is 
divided into the required proportion by the vertical cutwater, and 
is discharged into the user's flume which leads off to the right or 
runs out of the flume and into the company's ditch again. A flat 
crested weir set across both divisions of the flume and about three 
feet back from the entering end aids in the just division. In a struc- 
ture of this sort the dividing partition in the flume is so set that its 
distance from the water user's side of the box holds the same propor- 
tion to the whole width as the number of shares of stock owned by 
the water user holds to the number of shares below him plus those 
he holds himself. In the case as given above the user owned ten 
shares of stock. One hundred shares had to be served by the water 
in the canal. The partition in his box would then be built so that 
it stood 10/100 of the way across the box. He, of course, would re- 
ceive the water pouring through the narrower compartment. The 
hinged gate at the beginning of the user's flume will allow him to 
turn water into his ditch or back into the company's canal at will. 

Such a structure assumes that water flows with an equal velocity 
at all points in a stream. This is never or very seldom the case, for 
the water near the banks is necessarily slowed down by weeds, rocks 



Circular 250] 



MEASUREMENT OF IRRIGATION WATER 



31 



or irregular earth work of the banks and bottom. With such a box 
the water user will usually receive less water than he is entitled to, 
for his share is taken from an area of reduced velocity while the 
water running past him comes from the fastest-flowing part of the 
stream. 

A box such as that described above contains about 650 board feet 
of lumber. 



Note: Gate to bo 
'at this 
■post 
U**3'6' 




Fig. 15. Drawing of proportional division box. 
MECHANICAL. DEVICES FOR MEASURING WATER VOLUMETRICALLY 
It frequently is desirable that a measuring device should record 
the volume of water delivered to irrigators, rather than the rate of 
flow. Numerous mechanically recording devices have been designed 
to accomplish this, several of these being described below. Without 
discussing the individual merits of these devices, it may be said that 
although several of them are in use in California and are believed by 
those using them to be giving more or less satisfactory service, there 
are many practical difficulties involved in operating devices of this 
nature. It would, therefore, seem that when a mechanical device is 
selected for measuring individual farmer's deliveries of irrigation 
water, the practical limitations of the device chosen should be under- 
stood. This is desirable in order that care may be taken to provide 
the conditions necessary for satisfactory measurements, and also that 
the need for occasional tests of the operating accuracy of the devices 
may be appreciated. 



32 



UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 



EELIANCE METER 

The Reliance meter consists of a brass vane, shaped something 
like a propeller wheel, set in a throat, and a brass rod which connects 
the vane to the recording head. This recording head contains gear- 
ing which is connected with a counter. The figures in this counter 
show the number of acre-feet of water which have passed through 
the device. 




Fig. 16. Photograph of Reliance meter. 



This apparatus is set so that the water to be measured pours be- 
tween a series of plates or vanes and on to the propeller shaft in the 
throat. It can be used in either open ditches or concrete pipe lines. 

The great advantage of such a device lies in the fact that it shows 
at a glance how many acre-feet of water have passed through the 
meter. With most other devices some computations are necessary to 
change the expression of the flow in cubic feet per second into terms 
of acre-feet. 

Figure 16 is a photograph of a Reliance meter installed on a con- 
crete pipe line. 



Circular 250] 



MEASUREMENT OF IRRIGATION WATER 



33 



DETHRIDGE METER 

In the Keliance meter only a part of the stream hits the propeller 
wheel and turns it. In the Dethridge meter (Fig. 17) the whole 
flow of the stream is directed against the wheel. The wheel in this 
case is a large sheet-iron drum, three feet, four inches in diameter 
and two feet, six inches wide. Attached to the outer surface of this 
drum are a series of heavy blades which extend ten inches beyond 
the circumference of the drum. 




Fig. 17. Photograph of Dethridge meter. 

This drum turns in hardwood bearings attached to the concrete 
base. When the wheel turns the projecting blades fit closely into a 
depression in the concrete floor of the device. 

Water, when turned into the device, presses successively against 
the blades on the cylinder and turns it in the bearings. A counter 
can easily be arranged to record these revolutions. With a Dethridge 
meter of the size described above, the discharge per revolution is 
about 30.5 cubic feet of water, regardless of the speed at which the 
wheel revolves. Each wheel installed should be accurately calibrated 
to determine the quantity of water discharged by the wheel per 



34 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 

revolution. The Dethridge meter has been very popular in Australia 
where a large number are in use. The device has never been used 
for the practical measurement of water in California. A description 
of the Dethridge meter is included in this circular because it involves 
a new principle. 



OTHER MEASURING DEVICES 

The Lyman meter. Many mechanical devices have been invented 
and patented by which the flow over weirs can be read as a quantity 
in terms of acre-feet, in place of as a rate of flow as in cubic feet 
per second. One of the more recent of these devices is the Lyman 
meter. 

The Lyman meter consists of a small, delicately balanced brass 
turbine wheel, enclosed in a brass shell. This shell is attached to 
the down-stream face of a weir bulkhead and must be so set that a 
hole bored through the weir bulkhead and leading into the turbine 
shell shall have a fixed relation with the weir notch. On the up- 
stream side of the weir board is a brass tube in which carefully placed 
openings have been cut. This brass tube connects at its base with 
a short length of pipe which passes through the weir bulkhead and 
into the turbine shell. 

The holes in the brass tube on the up-stream side of the weir 
bulkhead are of such varying diameters that they separate a cer- 
tain definite proportion of the water from the stream going over the 
weir, no matter at what height the water may stand above the weir. 
This small flow passes down the tube, through the bulkhead and into 
the turbine shell, where it revolves the small turbine wheel. This 
wheel is geared to a counter in such a way that the quantity can 
be read directly on the face of the counter. 

Different sizes of turbine wheels and different calibrations on 
the up-stream tube are necessary for use with weirs of various types 
and various lengths of crest. 

The Sentinel meter. This meter is mounted in a 2-foot section of 
steel pipe designed to be set in an irrigation pipe line, the size of the 
meter and of the steel section depending on the size of such pipe line. 
A wheel or turbine set in the steel section turns as the water passes 
through the pipe line, the revolutions of the wheel being indicated by 
a counter set in a dial above the steel section, the gearing being so 
arranged that the quantity of water passing is directly indicated by 
the counter. 



CIRCULAR 250] MEASUREMENT OF IRRIGATION WATER 35 

The Vcnturi meter. The Venturi meter is a device for the ac- 
curate measurement of relatively large flows of water. This device, 
in irrigation systems, is confined to large diversions from main canals 
into laterals and not to the measurement of water from the lateral 
to the individual user. 

The Venturi flame. The Venturi flume is similar to the Venturi 
meter in theory. "Water in an open ditch is led into a structure 
through a narrow throat and out into the original channel. In pass- 
ing through this constricted cross-section, a difference in head above 
the device and in the throat always results. This difference in head, 
which may be determined as in the submerged orifice, is the measure 
of the amount of water which passes through the device. Tables 
and curves have been prepared to aid in determining the amount of 
water passing through the Venturi flume when the difference iu 
water level above and below the device is known. The difference 
in head which results when a stream of water passes through the 
Venturi flume may be so small that it is very difficult to measure it 
accurately. 

SUMMAEY 

Common devices for measuring irrigation water in California in- 
clude rectangular, Cipolletti, and triangular weirs, submerged ori- 
fices with fixed and with adjustable openings, various miner 's-inch 
boxes and hydrants, and numerous mechanical devices for registering 
the volume of water that passes through them. 

In cases where the water to be measured is free from silt and 
where the grade of the ditch is sufficient to allow for the required 
backing up of the stream, some type of weir is undoubtedly the most 
satisfactory device. 

A weir is accurate, cheap, easily installed and has no moving 
parts to get out of order. For small heads of water, a triangular or 
"V" notch weir is most accurate. For larger heads a rectangular 
weir is most satisfactory. A Cipolletti weir seems to have no ad- 
vantage over a rectangular weir; it is harder to construct and for 
this reason is liable to be more inaccurate than the simple rectangular 
weir. 

If the ditch grade at the required point of measurement is so 
flat that the necessary fall over a weir crest can not be provided, or 
if the water to be measured is so heavily charged with silt that a 
weir pond would rapidly fill up, a submerged orifice may be con- 
sidered the most satisfactory device. 



36 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 

A submerged orifice of fixed dimensions, if carefully installed and 
with careful measurements for the difference in head, will give fairly 
accurate results. Accuracy is necessarily sacrificed when wide fluc- 
tuations in the stream to be measured make it necessary to install 
an adjustable orifice. With the adjustable orifice the coefficient 
"C, M which is used in determining the discharge, varies with the 
area of the opening. Besides this indefinite value of "C" there is an 
added complication due to variation in individual boxes. The skill of 
the carpenter who builds the device may affect its discharge to a con- 
siderable extent under given conditions. At times an adjustable sub- 
merged orifice is the only device at all suited to the conditions which 
must be met. 

Miner 's inch boxes are used chiefly in the foothill orchard sec- 
tions and in the citrus sections of southern California. These are 
usually installed by the company furnishing the water. If carefully 
installed and proper conditions of measurement are maintained, they 
will give approximately correct results.